1. Field of the Invention
The present invention relates to the preparation of precursors composed of either or both polyimide and polybenzimidazole as organic precursors for producing monolithic porous carbon with density less than or equal to 1.0 g/cc; and the processes for producing monolithic porous carbon from either or both polyimide and polybenzimidazole precursors in the powder form. The present invention further relates to the processes for producing monolithic porous carbon derived from either or both polyimide and polybenzimidazole precursors having one or more than one metals dispersed therein. The present invention even further relates to the processes for producing carbon-carbon composite prepared from precursors comprising either or both polyimide and polybenzimidazole and activated carbon in the form of powders and/or fibers.
2. Description of Related Art
Monolithic porous carbon, which possess interpenetrating pore structure, high density, high surface area, suitable pore size, and well defined pore size distribution, are highly desirable as electrode materials for lithium batteries, electrochemical capacitors, fuel cells, as well as other electrochemical devices. The following description will be directed to disk products although it will be understood that other such products can be made from the porous carbon.
One approach to produce monolithic porous carbon disk is through sol-gel technologies. The sol-gel technology generally consists of preparation of gels from solution, drying the gel while minimizing the gel shrinkage. The pyrolysis of thin gel films yields porous monolithic carbon disks. RF carbon aerogel currently in the market as electrode material for supercapacitors is derived from resorcinol and formaldehyde organic precursors. RF carbon aerogel provide high surface area and narrow pore size distribution. Yet, the potential market of RF carbon aerogel as electrode and material for ultracapacitors and supercapacitors is severely limited by the low operating voltage of the capacitor (<=5V) and high manufacturing cost of monolithic RF carbon aerogel materials.
Another approach to produce monolithic porous carbon disks is from powders of porous polymeric precursors by compressing them into a monolith disk followed by pyrolysis. There are 2 obstacles in this approach. One is the compressibility of the polymer precursor and the other is the difficulty in retaining interpenetrating network of the pores during the compression process. U.S. Pat. No. 6,544,648 discloses a process for making monolithic carbon disks by compressing carbon black powder with high surface area under vacuum at temperatures at or beyond 800° C. and a pressure at or beyond 3000 psi. This approach produces carbon disks with more undesirable micro-pores with pore diameter less than 2 nm than the ones by the sol-gel approach. The compression of carbon powder under vacuum at 800° C. displays severe technical challenges and high manufacturing costs.
Yet, another approach to produce monolithic porous carbon is from carbon black powder consolidated in a matrix of a carbonized synthetic resin. U.S. Pat. Nos. 5,776,633; 5,172,307; and 5,973,912 described processes of producing such porous carbon-carbon composites. The synthetic resin is phenolic resin in the patents. Although this approach has the merit of low cost by using inexpensive carbon black powder it has the difficulty in retaining open pores of synthetic resin, thus reducing the efficiency of pore surface area.
Bearing in mind the problems and deficiencies of prior art, it is therefore an object of the present invention to provide monolithic porous carbon disks with high surface area, high pore volume, high surface activity, well defined pore structure and morphology, and good mechanical properties. It would also be desirable to provide a process for producing such monolithic porous carbon disks with significantly lower cost as compared to the ones currently in the market.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.